1. Field of the Invention
This invention relates generally to cameras, and more particularly to very small electronic camera modules. Even more particularly, the invention relates to a device and method for manually adjusting the focal field in small electronic camera modules.
2. Description of the Background Art
Cameras in general, and digital camera modules in particular are well known. Digital cameras commonly incorporate means for adjusting the focal field in order to allow a user to take sharp photos of close up objects, such as business cards or bar codes, as well as distant objects, such as landscapes or people.
In some cameras, the focal field is continuously adjustable over a predefined range. For example, the lens is mounted to a guide so that it can be displaced along the optical axis by an electrical or mechanical drive.
While continuously adjustable lens mechanisms facilitate precise focus at virtually any focal distance in the range, their complexity introduces a variety of disadvantages. One disadvantage is that electrical drive units require power, which shortens battery life. Another disadvantage is the increased number of parts and required assembly time, both of which contribute to the overall cost of the camera. The complexity also increases possible sources of failure and, therefore, results in a decreased reliability for the camera. Yet another disadvantage is that the complexity of the device increases the overall size of the camera.
In mid to lower quality cameras, many of these disadvantages can be at least partially alleviated by replacing the continuously adjustable lens mechanism with a lens mechanism that can be manually transitioned between a plurality of discrete focal positions. Because the lens is moved manually by the user between the various focal positions, the drive motor, linkages, etc. are unnecessary. Further, providing a plurality of discrete focal positions is beneficial, because it eliminates the need to focus the lens for each picture. Thus, a user can take average quality images with minimal effort and experience. Indeed, many digital images that are taken are relatively disposable and do not require a high quality image. For example, taking a picture of a phone number or an address on a business card does not require a very high quality photo, as long as the letters and/or numbers are legible.
Despite the advantages provided by the multiple discrete position, manually operated focus mechanism, this type of mechanism has not been successfully implemented in miniature camera modules, such as camera modules now incorporated into cellular telephones, hand-held personal digital assistants (PDAs), and the like. Problems arise due to the extremely small size; of such camera modules. For example, the components of miniature camera modules are many times smaller than a user's finger and are, therefore, difficult to manipulate. Further, the small components are fragile, and can be easily broken when being directly manipulated by a user. Further, the camera modules should be able to be mounted directly on a circuit board of the main device (cell phone, PDA, etc.), therefore access to the module is somewhat limited. Yet another problem is that it would be difficult to see what position the small lens is in at any given time. Yet another problem is that the camera modules must compete with the host device for allocated space, so focus mechanisms that require extra space would be considered a disadvantage. For any one or more of these reasons, or other reasons, known miniature camera modules do not include user adjustable focus mechanisms, or at least do not include such modules that do not suffer from one or more of the above described disadvantages.
What is needed, therefore, is a miniature camera module, with a user adjustable focus mechanism, that is more compact. What is also needed is a miniature camera module, with a user adjustable focus mechanism, that requires fewer components to function. What is also needed is a miniature camera module, with a user adjustable focus mechanism, that minimizes points of possible failure. What is also needed is a miniature camera module, with a user adjustable focus mechanism, that requires a shorter assembly time and is less expensive to manufacture. What is also needed is a miniature camera module, with a user adjustable focus mechanism that is easy for a user to manipulate manually. What is also needed is a miniature camera module, with a user adjustable focus mechanism, that provides clear indicia of the current focal position of the lens.